Circuit for electric-discharge devices



Nov. 1, 1927. 1,647,605

R. W. CHESNUT CIRCUIT FOR ELECTRIC DISCHARGE DEVICES Filed May 26. 1923 hue/72W W l l/Chesnui 35 as described above by the drop in potential Patented Nov. 1 927;

r 1,647,605 PATENT .OFF-ICE.L

ROY W. GHESNUT, OF EAST ORANGE, JERSEY, A SSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A'CORPORATION OF NEW YORK.

omourr Eon ELECTRIC-DISCHARGE ,nnvxcns.

Application filed May 26,

This invention relates to circuits for electric discharge devices such as vacuum tubes \of the three-electrode type. I i

An object of this invention is'to reduce noise in the vacuum tube circuit, due, for

example, to fluctuations in voltage or cur rent supplied to the tube for heating the filament or cathode.

The form of this inventionhereinafter de m scribed in detail is embodied 'in a vacuum tube repeater circuit of the type in which the negative grid potential is obtained by L the potential drop across/the terminal ofan impedance such as a resistance included in the circuitwhich supplies heating current to the cathode; The constancy of the directcurrent potential difference between the grid and the cathode will in such a case depend. upon the constancy of theheating current '20 supplied to the filament so that trouble may beexperienced if. the current supply fluctuates for any reason. v In'accordance with one form of this in- T vention, noise in" a vacuum tube transmission circuit due to cathode current fluctuations is substantially prevented by connecting the grid or control electrode effectively to the midpoint of the cathode for all alterr nating current components of the cathode current while connecting the control electrode to one side of the cathode for the direct current component of the heating current, thereby enabling the direct current pojtential of the controlelectrode to be obtained across the terminals of the resistance in the cathode heating circuit. One way this may be accomplished is by connecting the control electrode through a condenser to the midpoint 'of an impedance connected across the filament terminals and also by connecting the control electrode to one side of the cathode through a retard coil or other .device of high impedance to alternating current and low impedance to direct current.

"The drawing illustrates this invention em- 2 bodied in a transmission circuit employing a vacuum tube amplifier or repeater of the three-electrode type.

Referring in detail to the drawing, a vacuum tube 3 is disclosed having an anode 4, a cathode 5 and a grid or.control electrode 6; The input circuit for the tube compris+ ing control electrode 6 and cathode 5 is connected to an incoming line 8 by an input 1923. Serial No. 641,548.

step-up transformer 9, while the output circu1t comprising the anode 4 and cathode 5 is connected to an outgoing line 10 by an output transformer 11. .v Such anarrange ment as. is well known in the art enables the tube 3, to impress upon the outgoing line 10 currents corresponding to those present in line 8 but amplified in forin. The output circuit battery 12 is connected between the anode ,and cathode in the usual manner. The cathode 5 is heated by current from a suitable source of voltage 13. I i

Trouble in such a vacuum tube circuit is occasionally encountered due to cathode battery noise disturbing the circuit due to the cathode battery current actually changing rapidly by small amounts, which changes react upon the input circuit or the output circuit of the tube .to producealternating current potentials in the transmission ciring current potentialsfinj the transmission circuit is, of course, objectionable since .it 7

will be transmitted along with the amplified signals. The undesirable noise produced by fluctuations in the .cathodeheatin-g current is especially pronounced when the control electrode of the tube is maintained at a negative potentialwith respect to the oathode by a resistance drop in the cathode heat- 7 In t the vacuum tube circuit negative potential with respect to the oathode 5 by the voltage drop in the resistance,

cuit. The pr'esence of this foreign alternat across the terminals of resistance 14 also-' tends to fluctuate, and to thereby impress the fluctuations in potential upon the control electrode. and cause them to be amplified along with the signal currents received from the incoming line 8. w

In accordance with this invention, however, these undesirable fluctuations due to tained by the drop across the terminals of.

resistance 14:, in spite of the alternating current connection effectively to the midpoint of the cathode, the grid 6 is connected to the terminal of resistance 14 away from obtain the advantage of a resistance drop the cathode by. a path of high impedance to alternating current but of low impedance to direct current. In the drawing, this path is shown to comprise a retard coil'16'.

With the retard coil 16' and condenser 15 connected as shown, the control electrode will" still take the steady potential of the point 17 in the filament, heating circuit but any rapid fluctuations in the potential at the point 17 will not reach the grid 6 because the grid is connected to the point 17 through a retard coil or other apparatus of high impedance to alternating current and of low impedance to direct current. The grid will, of course,.take the instantaneous fluctuations in potential at the point of the circuitcorresponding to the midpoint of the filament because it is connected to thepoint 18- through a condenser 15 or other apparatus of low impedance to alternating current and of high impedance to direct current. .Bythis ar-v rangement, it is seen that it is possible, to.

in the filament heating circiut to provide a substitute for the-usual (3 battery and at the same-ti me having the grid connected to the midpo1nt of. the filamenttoreduce noise. J

It is to be understood, however, that this invention may possess other forms differing widely from the particular embodiment described above without departing in anywise from the spirit of this invention as defined in the appended claims.

The invention claimed is:

'1. An electric discharge device'having an anode, a cathode and a control electrode,

means for connecting said control electrode effectively to the midpoint of said cathode foralternating currentpotentials, and means for connecting said control electrode to one impedance to alternating current from said control electrode to one side of said cathode;

3..,In combination,- an electric *discharge T I device having an anode, a cathode and a con trol electrode, a, heatin current source for sa1d,cathode, a dlVld input circuit con necting, said control electrode and said said control electrode and said cathode, an

impedance connected in series circuit relation with said supply leads and between the control electrode and cathode in said input circuit, and a by-pass around said impedance comprising a condenser for preventing flucc tuations of the'current supplied by said supply leads to the cathode from changing the potential of the control electrode with re spect to the cathode. A

5; An electric discharge device having an anode, a cathode and a control electrode, heating current supply leads for said cathode, an input circuit connected between said control electrodeand said cathode, an impedance common to said supply leads and said input circuit, and a by-pass around said impedanceconnected eflectively ,to the niidpoint of said cathode, said by-pass being of high impedance to direct current. a

6. Anelectric discharge device having an anode, a cathode and a control electrode, current supply leads for supplying heating cur rent to saidcathode, an input circuit connecting said control electrode and said cathode'and comprising an impedance connected in series circuit relation with'said supply leads andbetween said cathode and control electrode, and means .comprising a circuit havingf'a high impedance to direct current for preventing'rapid; fluctuations in the heating current supplied to the cathode from substantiallytchangingthe potential of said control electrode with respect to the cathode.

7. In combination, an-electric discharge device havingean anode, a cathode and a control electrode, current supply leads for supplying heating currentoto said cathode,

an input circuit connecting said control electrode and said cathode comprising an impedance connected in said supply leads,

I s I means between said lmpedance and said control electrode of high impedance to alternating current and low impedance to direct current and a by-pass around said means and said impedance, said by-pass being of high impedance todire'ct current and low impedance to alternating current.

8. In combination, an "electric discharge device having an anode, a cathode and a control electrode, current supplyLleads for supplying heating current to said-cathode, an input circuit connecting said control electrode and said cathode comprising an impendance connected 1n said vsupply leads, means between saicLimpedance and said control electrode of high impedance to alternat-' 5 ing current and low impedance to direct current, and a by-pass around said impedance and said means connected effectively to the midpoint of said cathode.

'9. In combination, an electric discharge 10 device having an anode, a cathode and a-control electrode, current supply leads for supplying heating current to saidcathode, an input circuit connected to said control electrade and said cathode and comprising an terminals of said cathode and a condenserconnected around said first impedance and said retard coil and to the midpoint of said" second impedance.

In witness whereof, I hereunto subscribe my name this 24th day of May-A. 1)., 1923.

4 ROY W. CHESNUT, 

